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UNIVERSITY  OF  ILLINOIS 

Agricultural  Experiment  Station 


BULLETIN  No.  229 


DENDROPHOMA  LEAF  BLIGHT  OF  STRAWBERRY 


BY  H.  W.  ANDEHSON 


CONTENTS  OF  BULLETIN  No.  229 

PAGE 

INTRODUCTION    127 

SYMPTOMS   127 

ISOLATION  AND  CULTURAL  CHARACTERS 129 

MORPHOLOGY  AND  LIFE  HISTORY 129 

Mycelium    129 

Pycnidia  129 

Spores 131 

Conidiophores   131 

INFECTION  EXPERIMENTS   131 

HISTORY  OF  THE  DISEASE 132 

TAXONOMY  OF  THE  FUNGUS 134 

OTHER  LEAF-INHABITING  FUNGI  OF  THE  STRAWBERRY 135 

CONTROL  MEASURES  .  135 


DENDROPHOMA  LEAF  BLIGHT  OF  STRAWBERRY 

BY  H.  W.  ANDEKSON,  ASSISTANT  CHIEF  IN  POMOLOGY 

INTRODUCTION 

During  the  summer  of  1919  a  serious  leaf  blight  of  strawberry 
was  observed  in  several  localities  in  Illinois  and  Indiana.  At  first  it 
was  regarded  as  an  advanced  stage  of  the  ordinary  leaf  spot  caused 
by  Mycosphaerella  Fragariae  (Sehw.)  Lind.,  but  a  closer  examination 
showed  that  even  from  the  inception  of  the  attack  it  had  entirely 
different  symptoms.  A  more  detailed  study  revealed  the  presence 
of  fungus  fruiting  bodies  quite  distinct  from  those  of  the  leaf  spot. 
The  destructive  nature  of  the  disease  and  its  apparently  wide  dis- 
tribution seemed  to  warrant  a  more  extensive  study.  The  results  of 
this  investigation  are  given  in  the  following  pages. 

SYMPTOMS 

The  lesions  of  leaf  blight,  even  in  an  early  stage,  are  much  larger 
than  the  mature  lesions  of  the  ordinary  leaf  spot.  Usually,  only  one 
spot  appears  on  a  leaflet,  tho  there  may  be  from  two  to  five.  In  an 
advanced  stage  the  most  common  condition  is  a  V-shaped  dead  area 
extending  from  the  midrib  or  one  of  the  larger  veins  to  the  tip  or 
side  of  the  leaflet  with  the  apex  of  the  V  pointing  inward. 

The  young  spots  are  uniformly  reddish-purple  when  they  first 
appear  and  are  almost  circular  in  outline.  As  they  enlarge  the  cen- 
tral area  dies  and  becomes  brown.  Later,  three  zones  may  be  ob- 
served (Fig.  1)  :  (1)  an  outer  purple  zone  about  2-3  mm.  broad, 
which  gradually  shades  off  into  the  normal  green  of  the  leaf;  (2) 
a  light  brown  zone  about  5  mm.  broad;  and  (3)  a  central  dark  brown 
area  2-3  mm.  in  diameter  which  is  sometimes  covered  with  a  white 
granular  layer. 

On  the  under  surface  of  the  leaf  the  symptoms  are  the  same  ex- 
cept that  the  hairy  covering  masks  the  colors  and  makes 'them  ap- 
pear lighter  and  less  sharply  defined. 

When  the  spots  occur  between  prominent  veins  they  usually  re- 
main circular  in  outline  until  they  are  1-2  cm.  in  diameter.  If  they 
occur  on  a  prominent  vein,  and  especially  if  on  the  midrib,  they 
elongate  rapidly  and  become  elliptical  in  outline.  The  leaf  area  be- 
tween the  lesion  and  the  edge  of  the  leaflet  becomes  streaked  with 
purple,  the  color  being  especially  deep  along  the  veins.  Since  the 
veins  extend  in  a  fan-like  manner  from  the  point  of  infection,  the 
resulting  lesion  is  the  characteristic  V-shaped  discolored  area  de- 
scribed above.  This  area  of  leaf  tissue  remains  alive  for  some  time 
after  it  shows  the  purple  discoloration  but  finally  dies. 

127 


128 


BULLETIN    No.   229 


[July, 


FIG.  1. — STRAWBERRY  LEAF  BLIGHT  SHOWING  VARIOUS  TYPES  OF  LESIONS 
The  leaflet  in  the  upper  left-hand  corner  shows  a  typical  fan-shaped  dead 


When  the  spots  are  a  centimeter  or  more  in  diameter,  small  black 
dots,  the  pycnidia,  appear  scattered  over  the  central  dark  brown  area 
and  to  a  certain  extent  in  the  lighter  brown  zone  outside  of  this. 
These  dots  are  present  on  both  surfaces  of  the  leaflet  but  are  more 
evident  on  the  upper.  In  some  cases  the  pycnidia  do  not  appear  un- 
til a  large  area  of  the  leaflet  is  dead. 

In  1919,  the  diseased  areas  were  evident  as  early  as  the  first  of 
June,  but  it  is  not  known  how  much  earlier  they  may  appear.  They 
are  more  often  observed  on  the  older  leaves  but  are  not  uncommon 
on  young,  vigorous  leaves.  The  spots  continue  to  appear  thruout 


1920}  DENDROPHOMA  LEAF  BLIGHT  OF  STRAWBERRY  129 

the  summer  and  autumn.  Half  or  two-thirds  of  a  leaflet  may  die 
as  a  result  of  the  attack  and  often  entire  leaves  are  killed.  This 
results,  of  course,  in  a  loss  of  vigor  of  the  entire  plant. 


ISOLATION  AND  CULTURAL  CHAEACTERS 

Isolation. — In  order  to  determine  the  cause  of  leaf  blight,  the 
fungus  evident  on  the  diseased  parts  of  a  leaf  was  isolated  and  grown 
in  pure  culture.  Some  diseased  leaves  were  placed  in  a  moist  cham- 
ber for  several  days.  From  the  pyc»dia  abundant  spores  issued  in 
short,  thick  threads  (cirrhi).  Agar  plates  were  made  from  these  in 
the  usual  manner  and  single  spore  cultures  were  obtained.  Another 
set  of  cultures  was  obtained  by  crushing  the  pycnidia  on  sterile  slides 
and  pouring  plates.  In  both  cases  it  was  comparatively  easy  to  ob- 
tain pure  cultures.  Oat  agar  was  found  to  be  an  excellent  medium 
for  isolation  and  was  used  in  subsequent  studies  for  growing  the 
fungus.  The  cultures  were  kept  in  the  incubator  at  24°  C. 

Cultural  Characters. — No  extensive  study  of  cultural  characters 
was  made.  On  apple-bark  agar  the  fungus  formed  a  heavy,  white 
growth  which  was  closely  confined  to  the  medium.  The  aerial  my- 
celium was  scant.  Scattered  stromatic  masses  were  developed  in  most 
of  the  tubes.  There  were  usually  only  three  or  four  of  these  in  each 
tube.  Later,  several  pycnidial  chambers  were  formed  in  these  struc- 
tures with  ostioles  extending  in  various  directions,  thus  forming  a 
studded  structure  from  2-4  mm.  in  diameter.  The  spores  oozed  in 
quantities  from  the  ostioles  after  the  culture  was  two  weeks  old. 
Single  pycnidia  were  rarely  observed  on  apple-bark  agar ;  they  were 
more  common  on  plates  than  in  the  tubes. 

Spores  streaked  on  oat  agar  (Clinton's  formula)  resulted  in  a 
mycelial  growth  similar  to  that  described  above  but  even  more  closely 
confined  to  the  agar.  Abundant  single  pycnidia  were  formed  over  the 
surface  of  the  agar  within  a  week  and  the  spores  oozed  from  these 
in  great  abundance.  The  distinguishing  character  of  the  growth  in 
oat  agar,  aside  from  the  abundant  production  of  pycnidia,  was  the 
production  of  a  lemon-yellow  pigment  after  five  days.  This  was  first 
noticed  at  the  bottom  of  the  slant  but  it  gradually  spread  upward. 


MORPHOLOGY  AND  LIFE  HISTORY 

Mycelium. — The  hyphae  remain  light  colored  in  culture  for  a 
month  or  more.  There  are  no  pecularities  in  the  branching  or  type 
of  growth  by  which  the  fungus  can  be  distinguished.  In  the  leaf 
the  mycelium  penetrates  all  parts  of  the  tissue. 

Pycnidia. — The  pycnidia  develop  beneath  the  epidermis.  As  they 
grow,  the  epidermis  is  pushed  upward  and  finally  ruptured  in  a  star- 


130  BULLETIN   No.   229  [July, 

like  manner.  With  a  good  lens  the  segments  of  the  epidermis  may 
be  seen  pressed  against  the  surfaces  of  the  protruding  pycnidia.  The 
pycnidia  seem  to  be  embedded  more  deeply  in  the  tissues  on  the  lower 
surface  than  on  the  upper.  When  placed  under  moist  conditions, 
the  pycnidia  swell  to  several  times  their  normal  size  and  extend  well 
above  the  surface  of  the  leaf.  The  neck  of  the  pycnidium  is  conical, 
thus  making  the  entire  pycnidium  pear-shaped  rather  than  flask- 
shaped  (Fig.  2).  The  unusual  length  of  the  neck  of  the  pycnidium 


FIG.  2. — CROSS-SECTION  OP  A  DISEASED  LEAF,  SHOWING  THE  LOCATION 
OP  THE  PYCNIDIUM  AND  THE  EXTRUDING  NECK 
(Drawn  by  E.  F.  Guba) 

is  a  striking  characteristic  of  this  fungus  both  on  leaves  and  in  cul- 
ture, but  this  character  is  very  variable. 

The  wall  of  the  pycnidium  is  light  brown  under  high  magnifica- 
tion but  the  pycnidia  are  black  to  the  naked  eye.  The  walls  are  thin 
and  delicate  so  that  it  is  difficult  to  separate  the  pycnidia  from  the 
matrix  of  the  leaf  without  rupturing  them.  The  pycnidia  are  from 
200  to  300  microns  in  diameter. 

The  spores  issue  from  the  pycnidia  in  long,  thick,  gelatinous  cirrhi 
when  the  surrounding  atmosphere  is  moderately  humid.  In  about 
half  the  cases  observed,  the  cirrhi  did  not  arise  from  the  ostiole  but 
were  pushed  out  from  the  side  of  the  pycnidium.  A  few  cases  were 
noticed  where  two  cirrhi  originated  from  a  single  pycnidium,  one  on 
either  side  of  the  neck,  or  one  arising  from  the  ostiole  and  the  other 
from  the  side  of  the  pycnidium  near  the  base  of  the  neck.  When 
first  removed  from  a  moist  chamber,  the  cirrhi  are  thick  and  pearl 
colored;  as  the  leaf  dries,  they  shrink  markedly  and  are  honey  col- 


19&0]  DENDROPHOMA  LEAF  BLIGHT  OF  STRAWBERRY  131 

ored.    When  moist  they  are  easily  removed  on  the  point  of  a  needle, 
but  when  dry  they  are  hard  and  tightly  cemented  to  the  pycnidium. 

The  spores  exude  from  the  pycnidia  in  the  open  when  the  leaf 
becomes  moist.  During  a  dry  period  in  September,  spores  were -ob- 
served exuding  in  the  morning  after  a  moderate  dew,  thus  showing 
that  rains  are  not  necessary  to  supply  ^  sufficient  moisture  for  spore 
exudation. 

Spores — The  spores  are  hyaline,  continuous,  oblong-bacilloid,  or 
narrowly  ellipsoidal  (Fig.  3).    They  are  unusually  narrow  for  spores 
of  this  genus.     Two  or  three  large 
granules    usually    are    evident    at 


either  end,  thus  giving,  a  character-          ^         u         •      fl 
istic  appearance  (biguttulate)  to  the  <K  /?#  *L 

spores  under  the  high  power  of  the  y^f  j 

microscope.    Exuding  spores  on  the  "^ 

leaf  measure  5-7  X  1.5-2  microns, 
while  in  culture  they  are  slightly 

larger      Freshlv  oxndprl    snnrp^  arP          Fi£'  3'~ Dendroptomaobscurans. 
my  exuaea  spores  are     (a)    Branched  C0nidiophore;    (b) 

remarkably  constant  in  size,  rarely    Pycnospore 
varying  a  micron  in  length. 

The  spores  were  germinated  with  difficulty  in  hanging  drops  of 
tap  water.  In  agar  plates  only  about  1  percent  germinated.  No 
explanation  for  this  erratic  behavior  can  be  given.  The  pycnidia  will 
exude  spores  at  any  time  during  the  winter  or  spring  when  condi- 
tions are  favorable.  Leaves  were  brought  into  the  laboratory  every 
month  from  September  until  May,  and  when  placed  in  a  moist  cham- 
ber sodn  began  to  exude  spores  in  abundance.  Cultures  could  al- 
ways be  made  from  the  spores.  This  explains  a  possible  source  of 
infection  in  the  spring. 

ConidiopJiores. — These  are  peculiar  in  that  they  are  quite  long 
and  distinctly  branched.  (Fig.  3.) 

No  perfect  stage  of  the  fungus  was  found  altho  repeated  search 
was  made  on  old  leaves  during  the  spring.  This  stage  would  not 
be  necessary  in  the  life  history  of  the  fungus  since  the  pycnidia  live 
thruout  the  winter  and  produce  viable  spores  in  the  spring. 


Twelve  strawberry  plants  were  potted  and  all  but  the  very  young 
leaves  were  removed.  These  plants  were  allowed  to  grow  undisturbed 
for  three  weeks  and  during  this  period  no  signs  of  the  disease  ap- 
peared on  the  leaves.  Some  older  leaves  were  then  removed  and  the 
young  leaves  left  to  develop.  In  several  of  the  pots  runners  had 
been  sent  out  and  had  developed  new  plants  by  this  time.  Four  of 
the  plants  were  sprayed  with  a  suspension  of  spores  from  a  pure 
culture,  four  were  sprayed  with  a  suspension  of  spores  obtained  from 


132  BULLETIN  No.   229  [July, 

diseased  leaves,  while  the  remaining  four  were  sprayed  with  sterile 
tap  water.  The  pots  were  covered  with  bell  jars.  After  three  days 
the  bell  jars  were  removed  and  the  plants  kept  well  watered.  After 
ten  days  diseased  spots  appeared  on  several  leaflets  in  all  but  one 
of  the  pots  where  the  spore  suspensions  had  been  used,  while  none 
of  the  control  plants  showed  any  signs  of  the  disease. 

The  lesions  produced  were  typical  except  that  the  deep  purple 
color  was  absent,  probably  owing  to  the  lack  of  light  in  the  laboratory 
and  the  succulent  condition  of  the  plants.  It  was  expected  that 
numerous  lesions  would  appear  on  each  leaflet  inoculated,  but  as  a 
rule  there  were  only  two  or  three  and  on  about  50  percent  of  the 
leaflets  no  infection  was  evident.  In  some  cases  the  leaflets  blighted 
with  no  indication  of  a  definite  lesion  and  it  was  thought  that  these 
had  been  more  or  less  heavily  infected  but  that  they  had  wilted  so 
rapidly  and  completely  that  no  fruiting  bodies  had  been  produced 
on  them.  No  insects  were  observed  on  any  of  the  plants  from  the 
time  they  were  brought  into  the  laboratory.  Three  of  the  infected 
plants  died  about  ten  days  after  the  disease  first  appeared.  These 
were  discarded  since  the  cause  of  their  death  was  not  thought  to  be 
due  entirely  to  the  fungus  under  consideration. 

Two  plants  which  had  been  infected  with  spores  from  pure  cul- 
ture were  used  to  isolate  the  fungus.  From  the  edge  of  a  lesion  on 
one  of  these  plants,  a  pure  culture  was  obtained  from  the  mycelial 
growth  in  the  tissue.  Pycnidia  were  developed  on  the  lesions  of  two 
leaflets  of  the  second  plant  and  a  pure  culture  was  obtained  from 
the  exuded  spores. 

HISTORY  OF  THE  DISEASE 

In  1893,  Halsted1  reported  ' '  a  new  strawberry  blight ' '  as  follows : 
"Mr.  F.  L.  Stevens,  in  1892,  while  a  special  student  in  my  laboratory 
•and  upon  a  visit  to  his  home  in  Syracuse,  New  York,  obtained  speci- 
mens of  a  blight  upon  strawberry  leaves  which  has  been  under  in- 
vestigation since  that  date,  and  upon  which  the  following  report  is 
made."  He  then  describes  the  symptoms,  which  correspond  closely 
to  those  given  above,  and  states  that  the  disease  was  found  in  several 
points  in  New  Jersey  as  well  as  in  the  neighborhood  of  Syracuse,  New 
York.  He  believes  that  the  fungus  causing  the  trouble  belongs  to 
the  genus  Aposphaeria.  He  calls  attention  to  the  differences  between 
this  -fungus  and  Phyllosticta  fragaricola  Desm.  and  Rob.,  which  he 
states  is  a  European  species.  The  fungus  is  described  in  some  de- 
tail and  attention  called  to  the  prominent  pycnidium.  A  recognizable 
figure  of  the  disease  is  included.  From  the  description  of  the  symp- 
toms and  the  figure  presented,  there  is  no  question  but  that  this  is 

'Halsted,  B.  D.  Diseases  of  the  Strawberry.  New  Jersey  Agr.  Exp.  Sta. 
Ept.  14,  327-332.  1893. 


DENDROPHOMA  LEAF  BLIGHT  OF  STRAWBERRY  133 

the  disease  under  consideration.  He  calls  attention  to  the  biguttulate 
spores,  the  prominent  neck  of  the  pycnidium,  and  the  typical  V- 
shaped  diseased  area.  He  regarded  the  pycnidium  as  superficial  and 
hence  placed  the  fungus  in  the  genus  Aposphaeria — a  natural  mis- 
take when  one  does  not  have  sections  of  the  pycnidia  to  examine. 

The  fact  that  the  fungus  resembles  a  Phyllosticta  naturally  raises 
the  question  as  to  whether  or  not  it  is  the  same  as  Phyllosticta  fraga- 
ricola  Desm.  and  Rob.  The  spore  sizes  correspond  closely  but  in 
other  respects  there  is  a  decided  difference.  Two  exsiccati  specimens 
of  Phyllosticta  fragaricola,  Koumeguere  's  Fungi  Selecti  No.  1327  and 
Rabenhorst's  Fungi  Europaei  No.  1758,  in  the  herbarium  of  the  De- 
partment of  Botany,  University  of  Illinois,  were  examined.  In  both 
cases  it  was  at  once  evident  that  the  disease  caused  by  this  fungus 
is  entirely  different  from  the  blight  under  consideration.  The  spots 
were  much  smaller,  rarely  exceeding  3  mm.,  with  a  striking  white 
center.  The  disease  caused  by  Phyllosticta  fragaricola  more  nearly 
resembles  our  strawberry  leaf  spot  (Mycosphaerella  Fragariae  (Schw.) 
Lind.)  but  the  lesions  are  smaller  and  the  centers  whiter.  Phyllosticta 
fragaricola  is  reported  from  London,  Ontario,1  and  is  common  in 
Europe. 

In  1894,  Ellis  and  Everhart  described  a  new  fungus  on  cultivated 
strawberry  which  they  called  Phoma  obscurans.2  The  description 
given  by  them  is  as  follows: 

"Spots  5-8  mm.  in  diameter  with  ferruginous  center  and  broad  purple 
border,  paler  below,  perithecia  few,  scattered,  convex  prominent.  Sporules  ob- 
long elliptical,  hyaline,  2  nucleate,  4.5  -  5.5  X  1.5-2  microns.  Basidia  simple, 
lanceolate,  fusoid,  8-12  X  1.5  microns. 

"Phyllosticta  fragaricola  Desm.  has  similar  sporules  but  the  spots  are  much 
smaller  with  a  white  center.  The  basidia  also  indicate  Phoma  and  not  Phyllosticta. 

"On  leaves  of  Fragaria  (cult.)  Nuttallburg,  West  Virginia  and  Newfield, 
New  Jersey." 

The  above  description  was  repeated  by  Millspaugh  and  Nuttall  in 
' '  Flora  of  West  Virginia ' '  in  1896.3  They  give  the  type  habitat  ' '  On 
leaves  of  Fragaria  cult.  July  8,  1894." 

Two  exsiccati  specimens  of  Phoma  obscurans  E.  &  E.,  in  the 
herbarium  of  the  Department  of  Botany,  University  of  Illinois,  in 
Ellis  and  Everhart 's  North  American  Fungi,  were  examined.  No. 
3258  has  the  following  label:  "Phoma  obscurans  E.  &  E.,  Proc.  Acad. 
Nat.  Sci.  Phil.,  1894,  p.  357.  On  leaves  of  cultivated  strawberry, 
Nuttallburg,  West  Virginia,  Nov.,  1894,  L.  W.  Nuttall."  In  this 
packet  there  are  two  leaflets  with  rather  large  spots  in  every  way 
similar  to  those  of  the  disease  under  consideration.  No.  3444  has 


aNotae  mycologicae.     Ann.  Mycol.,  11,  546-568.     1913. 
2Proc.  Acad.  Nat.  Sci.,  Philadelphia,  1894,  p.  357.     1895. 
"Millspaugh,    G.   F.,   and    Nuttall,   L.   W.     Flora   of    West   Virginia.     Field 
Columbian  Museum  Publications,  Botanical  Series,  1   (1896),  107. 


134  BULLETIN   No.   229  [July, 

the  following  label:  "Phoma  obscurans  E.  &  E.,  Millspaugh  and 
Nuttall,  Flora  of  West  Virginia,  1896,  p.  107.  On  leaves  of  culti- 
vated strawberry,  Nuttallburg,  West  Virginia,  Sept.  1895,  L.  W. 
Nuttall."  There  are  three  leaflets  in  this  collection,  each  showing 
one  dead  area  of  the  typical  triangular  form  on  which  abundant 
pycnidia  are  present. 

The  description  of  Ellis  and  Everhart  is  brief  and  the  size  of 
the  spots  here  indicated  is  much  smaller  than  the  average  found  in 
the  field.  The  exsiccati  specimens  show  the  spots  much  larger  in 
most  cases  than  indicated  by  the  description. 

A  fragment  of  a  leaflet  from  specimen  No.  3444  was  secured  and 
from  it  a  microscopic  mount  was  made  and  spore  measurements  se- 
cured. The  spore  measurements  and  general  character  of  the  spores 
and  pycnidia  agreed  closely  with  material  from  collections  of  the 
writer.  The  spore  lengths  given  by  Ellis  and  Everhart  are  somewhat 
less  than  those  made  by  the  writer  from  his  material. 

There  is  no  question  but  that  the  disease  described  by  Ellis  and 
Everhart  is  the  same  as  the  leaf  blight  under  consideration.  It  is 
evident  that  three  collections  were  made,  two  by  Nuttall  in  West 
Virginia  (July  8,  1894,  and  September,  1895)  and  one  in  Newfield, 
New  Jersey,  at  an  unrecorded  date,  but  during  6r  before  the  year 
1894. 

TAXONOMY  OF  THE  FUNGUS 

It  has  been  customary  to  restrict  the  genus  Phoma  to  those  species 
of  the  Sphaerioidaceae-Hyalosporae  occurring  on  stems  while  leaf 
parasites  are  placed  in  the  genus  Phyllosticta.  Ellis  and  Everhart 
referred  the  species  under  consideration  to  Phoma  rather  than  to 
Phyllosticta  on  the  basis  of  conidiophore  characters.  Just  what  con- 
stituted the  basis  of  this  distinction  is  not  clear  from  their  description. 

Halsted  called  the  fungus  Aposphaeria  on  account  of  the  sup- 
posedly superficial  pycnidia.  It  is  evident  from  Fig.  2  that  the 
pycnidia  are  by  no  means  superficial.  Aposphaeria  has  short,  un- 
branched  conidiophores  while  in  this  species  the  conidiophores  are 
distinctly  branched. 

Saccardo1  erected  the  genus  Dendrophoma  to  include  all  Phoma- 
like  species  having  branched  conidiophores.  This  genus  is  ordinarily 
described  as  having  a  papillate  ostiole  while  the  species  under  con- 
sideration has  a  rather  long-necked  pycnidium,  which  might  be  called 
rostrate.  Spaeronema  has  as  one  of  its  distinguishing  characters  a 
rostrate  pycnidium,  but  the  neck  of  this  genus  is  very  long  and  the 
conidiophores  are  unbranched.  Therefore,  it  would  appear  that  the 
species  under  consideration  has  characters  of  both  Dendrophoma  and 
Sphaeronema.  On  account  of  the  fact  that  the  neck  is  comparatively 


2,  4.     1880. 


DENDROPHOMA  LEAF  BLIGHT  OF  STRAWBERRY  135 

short  and  the  conidiophores  are  branched,  the  writer  is  of  the  opinion 
that  this  species  should  be  placed  in  the  genus  Dendrophoma  and 
proposes  the  new  combination  Dendrophoma  obscurans.1 


OTHER  LEAF-INHABITING  FUNGI  OF  THE  STRAWBERRY 

The  common  leaf  spot  of  strawberry  due  to  Mycosphaerella  Fra- 
gariae  (Schw.)  Lind.  is  the  only  other  widely  distributed  leaf  dis- 
ease in  Illinois.  Ascochyta  Fragariae  Sacc.  is  reported  as  common 
in  New  York.  This  fungus  produces  a  subcircular  purple  spot  which 
becomes  white  with  a  dark  purple  margin.  Ascochyta  Fragariae  has 
not  been  found  in  Illinois. 

In  May,  1883,  Earle  collected  a  fungus  on  strawberry  leaves  at 
Anna,  Illinois,  which  Ellis  and  Everhart  described  as  Septoria 
aciculosa.2  No  further  mention  of  this  fungus  could  be  found  by 
the  writer.  In  April,  1920,  Mr.  E.  F.  Guba,  an  assistant  in  the  De- 
partment of  Horticulture,  sent  some  dead  leaves  of  cultivated  straw- 
berry plants  to  the  writer  from  near  Anna  for  identification  of  the 
fungus  occurring  on  their  surfaces.  This  proved  to  be  the  same 
Septoria  aciculosa  E.  &  E.,  collected  thirty-seven  years  previously 
in  this  same  locality.  It  has  since  been  found  to  be  widely  distrib- 
uted in  this  state.  This  fungus  appears  in  dead  or  dying  leaves  of 
the  previous  season  and  there  is  no  reason  to  believe  that  it  is 
parasitic  in  nature  altho  most  species  of  Septoria  are  classed  as  para- 
sites. The  distinguishing  character  of  this  fungus  on  the  leaves  is 
the  presence  of  relatively  large  black  spots,  .5-1  mm.  in  diameter, 
which  resemble  small  sclerotia.  Under  a  lens  these  appear  to  be 
composed  of  grouped  pycnidia  as  described  by  Ellis  and  Everhart. 

CONTROL  MEASURES 

No  experiments  on  the  control  of  leaf  blight  were  attempted  in 
connection  with  this  study.  While  the  disease  causes  serious  loss  of 
functioning  leaf  tissues,  it  is  not  considered  of  sufficient  economic 
importance  to  warrant  spraying  or  other  expensive  control  measures. 
Since  infection  evidently  takes  place  thru  the  greater  part  of  the 
growing  season,  it  would  be  necessary  to  spray  over  a  relatively  long 
period. 

^Dendrophoma  obscurans  nov.  comb.  Spots  large,  .5-3  cm.  or  more ;  circular, 
oval,  or  sometimes  fan-shaped;  brown  with  broad  purple  zone.  Pycnicia  scat- 
tered, amphigenous,  flask-shaped,  150  -  300  microns,  erumpent.  Pycnosporcs 
hyaline,  continuous,  bacilloid  or  narrowly  ellipsoidal,  biguttulate,  5  -  7  X  1.5  -  2 
microns.  Conidiophores  long,  branched.  On  living  leaves  of  cultivated  straw- 
berry. 

2Torr.  Bui.,  11,  73.     1884. 


136  BULLETIN   No.   229  [July,  1920} 

The  practice  of  mowing  the  leaves  of  the  old  vines  and  cultivating 
after  harvest  is  believed  to  reduce  the  amount  of  trouble  from  this 
blight.  On  a  patch  where  mowing  was  done  the  new  leaves  and 
young  plants  appeared  almost  free  of  the  disease  during  the  latter 
part  of  the  growing  season. 

The  practice  of  spraying  strawberries  for  the  common  leaf  spot 
and  insect  troubles  has  not  become  general  in  Illinois  and  unless  more 
extensive  damage  should  be  done  by  this  leaf  blight  in  the  future,  it 
would  not  be  considered  advisable  to  make  special  applications  of 
spray  mixture  for  its  control. 


UNIVERSITY  OF  ILLINOIS-URBANA 


